The field of art to which this invention pertains is the simultaneous hydrocracking of multiple feedstocks. Petroleum refiners often produce desirable products, such as turbine fuel, diesel fuel and other products known as middle distillates, as well as lower boiling hydrocarbonaceous liquids, such as naphtha and gasoline, by hydrocracking a hydrocarbon feedstock derived from crude oil or heavy fractions thereof. Feedstocks most often subjected to hydrocracking are the gas oils and heavy gas oils recovered from crude oil by distillation. A typical heavy gas oil comprises a substantial portion of hydrocarbon components boiling above 371° C. (700° F.) usually at least about 50% by weight boiling above 371° C. (700° F.). A typical vacuum gas oil normally has a boiling point range between 315° C. (600° F.) and about 565° C. (1050° F.).
Hydrocracking is generally accomplished by contacting in a hydrocracking reaction vessel or zone the gas oil or other feedstock to be treated with a suitable hydrocracking catalyst under conditions of elevated temperature and pressure in the presence of hydrogen so as to yield a product containing a distribution of hydrocarbon products desired by the refiner. The operating conditions and the hydrocracking catalyst within a hydrocracking reactor influence the yield of the hydrocracked products.
Traditionally, the fresh feedstock for a hydrocracking process is first introduced into a denitrification and desulfurization reaction zone particularly suited for the removal of sulfur and nitrogen contaminants and subsequently introduced into a hydrocracking zone containing hydrocracking catalyst. Another method of hydrocracking a fresh feedstock is to introduce the fresh feedstock and the effluent from the hydrocracking zone into the denitrification and desulfurization zone. The resulting effluent from the hydrocracking zone is separated to produce desired hydrocracked products and unconverted feedstock which is then introduced into the hydrocracking zone.
Although a wide variety of process flowschemes, operating conditions and catalysts have been used in commercial activities, there is always a demand for new hydrocracking methods which provide lower costs, higher liquid product yields, higher quality products and the ability to simultaneously process a variety of different hydrocarbon feedstocks.